Vera: No cartridge firearm (and Vera is obviously one) needs "air around her" to fire. Every cartridge has everything it needs right inside it. Guns can be fired in vacuum, and even underwater. It's been tried and proven. This was just a case of writers not knowing shit about something.

The writers do likely know how their fictional weapons that only exsist in the future work.

Despite what the prop gun is in the real world what it is in the context of the show is entirely different. Unless McCoy really did repair Chekov's artery with a piece from an AMT model of a Klingon battle cruiser and the Mr. Fusion energy device on the DeLorean is really a coffee grinder.